Anti-skid control system

ABSTRACT

In the anti-skid system disclosed, a vehicle&#39;&#39;s wheel is protected from skidding in response to rapid acceleration, by comparing the wheel velocity with a reference signal that follows the wheel velocity but only within a predetermined maximum rate of velocity rise, and by then attenuating the wheel&#39;&#39;s drive to slow its acceleration. According to one embodiment of the invention a wheel velocity voltage generator generates a wheel velocity signal. An operational amplifier responding to the wheel velocity signal and an integrating circuit establish the reference signal that can rise up to a predetermined rate. A comparator derives an output signal when the rise rate in the wheel velocity signal exceeds the maximum rise rate of the reference signal. The output signal releases a free-running multivibrator that periodically interrupts power to the ignition system so the latter attenuates the wheel acceleration.

United States Patent 1 1 Q Arai et al.

[ Dec.4,1973

[ 4] ANTI-SKID CONTROL SYSTEM [75] Inventors: HiroshiArai; Jun Ohta,both of Toyota, Japan [73] Assigneez Toyota Jidosha Kogyo KabushikiKaisha, Toyota-shi, Aichi-ken, Japan [22] Filed: July 16, 1971 [21]Appl. N0.: 163,349

[30] Foreign Application Priority Data I 303/20, 21 P, 21 BE, 21 CF;317/5; 246/167 R; 105/61; 340/53 Lueck et al 303/21 BE 3,558,197 l/l97l3,560,759 2/1971 Buehler et a1. 105/61 X 3,627,074 12/1971 Burckhardt180/82 3,663,070 5/1972 Scharlack 303/21 P Primary Examiner--Kenneth H.Betts Att0rneyl) avid Toren et al.

[57] ABSTRACT In the anti-skid system disclosed, a vehicles wheel isprotected from skidding in response to rapid acceleration, by comparingthe wheel velocity with a reference signal that follows the wheelvelocity but only within a predetermined maximum rate of velocity rise,and by then attenuating the wheels drive to slow its acceleration.According to one embodiment of the invention a wheel velocity voltagegenerator generates a wheel velocity signal. An operational amplifierresponding to the wheel velocity signal and an integrating circuitestablish the reference signal that can rise up to a predetermined rate.A comparator derives an output signal when the rise rate in the wheelvelocity signal exceeds [56] References Cited UNITED STATES PATENTS fiTt ligil'Li'e iel l fi. liiifgiifiifivififii 1:: 2,842,103 7/1958Safldl$m 180/82 periodically interrupts power to the ignition system so3,356,082 12/1967 Jukes 317/5 x the latter attenuates the wheelacceleration 3,401,984 9/1968 Williams et al. 303/2] BE 3,496,535 2/1970Tyzack 180/82 X 42 Claims, 4 Drawing Figures V--... IC

f I f 2 E VELOCITY VELOCITY VOLTAGE f 5 f 6 SENSOR GEN 1 COMPA- IGNITIONIGNITION 1 CONTROL I I VOLTAGE ENG NE E GEN I 1, A ,I

DRWE I WHEElcS A] N i PMENTH] DEC 4 I975 3.776.357 SHEET 10F 2 FIG. I {Cl 2 f f E VELOCITY N322 4 r f f SENSOR GEN l COMPA- IGNITION IGNITION YCONTROL REF RATOR CKT con. G'EF w D ENGINE L3 WHEELS 2mm FIG. 2

WHEEL VELOCITY (VOLTAGEIQ VELOCITY (VOLTAGE) b I IGNITION, O CONTROL GM1 (EXTINCTION) OFF INVENTOR s HIRosIII IIIIIII HIM OHTH PATENTED DEB 4I975 SHEET 2 0F 2 o zoEzQ VVENTORS W205!!! men,

.JUM earn 1%, W/QZ ANTI-SKID CONTROL SYSTEM REFERENCE TO COPENDINGAPPLICATION This application is related to the copending application ofTakeshi Oehiai, Ser. No. 109,465, filed Jan. 25, 1971 now abandoned forSKID CONTROL SYSTEM. It is also related to the application of TakeshiOchiai, Ser. No. 109,461, filed Jan. 25, 1971 now abandoned for SKIDCONTROL SYSTEM FOR VEHICLES.

BACKGROUND OF THE INVENTION This invention relates to anti-skid systemsfor vehicles, particularly for preventing the wheels of vehicles such asautomobiles from slipping when sudden acceleration is applied to startsuch vehicles or to speed them up. I

When a vehicles wheels are rapidly accelerated at the time the vehicleis started or while the vehicle is traveling and the driving torque fromthe engine substantially exceeds the torque of the reaction forceapplied by the ground engaging the surface of the wheel, the so-calledtire torque, the driven wheel will slip and run idle. This wheel idlingis most likely to develop when the coefficient of friction between thetire and the road surface is small. This is the case when the vehicle istraveling on a gravel road, a snow covered road, a frozen road, or thelike. Under such conditions, the resistance of the wheel to lateraldisplacement of the vehicle is decreased. The vehicle may respond withirregular turns or by spinning around.

An object of this invention is to prevent wheel slips regardless of theamount of acceleration applied by the accelerator pedal.

Another object of the invention is to prevent the be fore mentionedproblems.

SUMMARY OF THE INVENTION According to a feature of the invention, theaboveidentified disadvantages are obviated and the objects obtained, bycomparing the velocity of a wheel with a reference signal that followsthe wheel velocity but only up to a predetermined rate of velocity rise,and by then attenuating the wheels drive to slow its acceleration.

According to another feature of the invention the wheels acceleration isslowed by interrupting the emission of engine ignition sparks. Accordingto another feature of the invention the wheel acceleration is slowed bystopping the fuel supply to the engine. This prevents the generation ofuseless engine torque which causes slippage of the wheels and idlerotation.

According to yet another feature of the invention, wheel velocitygenerating means generate a velocity signal corresponding to thevelocity of the wheel. Reference means responsive to the generatingmeans establish a reference signal that corresponds to the velocity ofthe wheel and increases at a predetermined rate when the wheel velocitysignal exceeds the predetermined rate. Comparator means respond to thegenerating means and the reference means to generate a comparison signalcorresponding to the comparison of the reference signal and the velocitysignal.

According to still another feature of the invention the reference meansincludes an operational amplifier for comparing the beforementionedreference signal and the wheel velocity signal, and another operationalamplifier for determining the reference signal by integrating the wheelvelocity signal upon receipt of the output signal of the operationalamplifier.

According to still another feature of the invention, the control meansinclude a free-running multivibrator which operates in response tosignals indicating that the rate of velocity rise exceeds thepredetermined rate and causes a circuit to interrupt the primary currentof an ignition coil of the vehicles engine.

These and other features of the invention are pointed out in the claims.Other objects and advantages of the invention will become known from thefollowing detailed description when read in light of the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of ananti-skid system used in a vehicle and embodying features of theinvention;

FIG. 2 is a graph illustrating the velocity of a wheel with respect totime in the system of FIG. 1 for the purpose of explaining the operationof the anti-skid device of FIG. 1;

FIG. 3 is a schematic diagram of an anti-skid system used in a vehicleand embodying features of the invention; and

FIG. 4 is a voltage-time graph for explaining the operation of thesystem in FIG. 3.

DESCRIPTION OF PREFERRED EMBODIMENTS In FIG. 1, a wheel velocity sensor1 detects the wheel velocity of a driving wheel by means of a rotationdetector installed on each wheel, a speed meter installed on the outputshaft of a transmission for measuring the number of rotations, or thelike. The sensor derives electrical signals which vary linearly with thevelocity of the driving wheel.

A wheel velocity voltage generator 2 generates a wheel velocity voltagecorresponding to the wheel velocity detected by the wheel velocitysensor 1. In response to signals from the wheel velocity voltage generator 2, a reference voltage generator 3 produces a reference voltagewhich corresponds to the wheel velocity voltage as long as the rise rateof the wheel velocity voltage remains below a predetermined maximum. Thereference voltage generator 3 establishes a maximum rate of rise. Whenthe wheel velocity voltage exceeds that rise rate the reference voltagegenerator 3 stops following but rises only at the maximum rate. Acomparator 4 compares the wheel velocity voltage from the generator 2and the reference voltage from the generator 3. It derives an outputvoltage when the wheel velocity voltage exceeds the reference voltage.This of course occurs when the velocity voltage rise rate exceeds themaximum rise rate. An ignition control circuit 5 interrupts engineignition sparks from an ignition coil 6 when the output voltage isderived from the comparator 4.

The system of FIG. 1 forms part of an automobile C having the usualinternal combustion engine E, wheels W, and drive train D, etc.

The principle of operation of the above-described anti-skid system isillustrated in FIG. 2. Here the abscissa represents time and theordinate represents the wheel velocity and the reference velocity aswell as the operating condition of the ignition control circuit 5. The0rdinate may also be considered to represent the wheel velocity voltageand the reference voltage since these are linearly related to thecorresponding velocities.

At time 2 an accelerator pedal accelerates the engine E through athrottle valve. The wheel velocity increases as shown by the curve a. Acorresponding wheel velocity voltage which conforms to the wheelvelocity is generated by the wheel velocity generator 2. This voltagemay also be considered as being represented by the curve a. At this timethe reference voltage generator 3 follows the voltage of the wheelvelocity as long as it does not exceed the critical acceleration ormaximum acceleration established by the generator 3. This maximumacceleration or maximum rate of rise in reference voltage is shown bythe curve b. It represents a maximum acceleration produced by thedriving torque from the engine that can be expected to allow the tire tokeep gripping the road surface. The generator 3 thus generates thereference voltage which changes according to the way the velocitychanges within this maximum acceleration. When the wheel accelerationexceeds the maximum acceleration set, the reference voltage rises at themaximum rate only.

When the increase in the rate of the wheel velocity as indicated by thewheel velocity voltage, makes the wheel velocity higher than the risingreference velocity as indicated by the reference voltage at the time tthe comparator 4 derives an output voltagein accordance with thedifference between the magnitude of both voltage signals. As a result ofthis output the control circuit 5 is turned on to extinguish theignition coil 6. As a result the wheel velocity that was increasingstarts to drop.

At the time the wheel velocity becomes less than the reference wheelvelocity. That is to say at the time t the wheel velocity drops belowthe reference voltage. The comparator 4 then stops producing an outputvoltage. This turns off the control circuit 5. The inertial forceinherent in the wheel system starts the engine again at this time so asto accelerate the wheels again.

The acceleration and deceleration described above is repeated. Finallythe wheel velocity change follows the reference wheel velocity change.Thus the wheel is accelerated without slip.

The above operation is identical whether the potential wheel slip ariseswhile the vehicle is standing still or while the vehicle is moving at aconstant velocity. [f the anti-skid system according to this inventionwere not employed the wheel velocity would rapidly increase as shown bythe curve a. This would cause wheel slip. The vehicle body would not beaccelerated at all.

In the embodiment illustrated in FIG. 3, a wheel velocity voltagegenerator generates a DC voltage having a linear relation with respectto the rotational speed of the driving wheel as described above. Anoperational amplifier having a negative-phase input terminal 21 and agrounded positive-phase input terminal 22 as well as an output terminal23 forms an operational integrator with an input resistor 24 and anintegrating feedback capacitor 25. The negative-phase input is biased toa negative voltage by a voltage divider composed of resistors 26 and 27connected between ground and a negative voltage Vcc. The resistor 24 andcapacitor integrate the voltage at the junction of resistors 26 and 27.A positive voltage +Vcc energizes the operational amplifier 20 with apositive potential. The source Vcc furnishes negative potential to theamplifier 20.

In a second operational amplifier 30 a negative-phase input terminal 31receives the DC voltage from the generator 10. A positive-phase inputterminal 32 serves as another differential input terminal in theoperational amplifier 30. The terminal 32 receives its input from theoutput terminal 23 of the operational amplifier 20. The voltages +Vccand Vcc serve as supply voltages for the operational amplifier 30.

If the positive-phase input potential exceeds the negative-phase inputpotential, the value +Vcc is obtained at an output terminal 33 of theamplifier 30. If the negative-phase input potential exceeds thepositivephase input potential the value Vcc is obtained at the terminal33.

A feedback circuit composed of a diode 34 and a resistor 35 in seriestherewith passes positive voltages appearing at the output terminal 33to the negative-phase input terminal 21 of the amplifier 20. Thepositive phase input terminal 32 of the amplifier 30 is connected to theoutput terminal 23 of the amplifier 20.

When the DC voltage is generated by the wheel velocity voltage generator10, the potential at the negative-phase input terminal 31 of theoperational amplifier 30 exceeds that of the positive phase inputterminal 32. This decreases the potential at the output terminal 33 toVcc. As a result the diode 34 is driven into nonconduction. Thepotential to be applied to the negative-phase input terminal 21 of thefirst operational amplifier 20 becomes negative by a value correspondingto the potential obtained by dividing the supply voltage Vcc between theresistor 26 and 27. On the other hand, the grounded positive phase inputterminal 22 tends to increase the potential of the output terminal 23 tothe +Vcc.

Now if the potential at the negative phase input terminal 21 is e andthe potential at the output terminal is 2,, then The resistance value ofthe resistor 24 is R and the electrostatic capacitance of the capacitor25 is C.

The capacitor 25 is charged to e with the polarities illustrated. If e,-is constant the rate of increase of the voltage at the output terminal23 is determined by the time constant CR. The potential of the outputterminal 23 that is increased after being set as described above isapplied to the positive-phase input terminal 32 of the secondoperational amplifier 30. When the potential exceeds the potential atthe negative phase input terminal 31 the potential at the outputterminal 33 of the second operational amplifier 30 changes over to +Vcc.This causes the diode 34 to conduct.

The voltage obtained by distributing the supply voltage Vcc over theresistors 26, 27 and 24 is then applied to the negative-phase inputterminal 21 of the first operational amplifier 20. Because theresistance value of the resistor 27 is smaller than that of the resistor26, the potential at the negative-phase input terminal 21 exhibits apositive value. The output terminal 23 thus discharges the electriccharge on the capacitor 25 in an effort to become a negative potential.However, the time constant of the discharge is far smaller than thatduring charging. Therefore, the voltage set by the capacitor 25 at theoutput terminal 23 remains almost constant.

When the potential at the output terminal 23 of the operationalamplifier 20 becomes lower than the at the negative-phase input terminal31 of the amplifier 30 the potential at the output terminal 33 againdrops to Vcc. This charges the capacitor 25 as described above andmaintains the voltage at a constant value.

As long as the wheel velocity voltage is maintained at a constant valuethe voltage identical to this wheel velocity voltage is memorized at theoutput terminal 23 of the first operational amplifier 20. When the wheelvelocity voltage rapidly increases and the rate of change thereofexceeds the value determined by the time constant CR the voltage at theoutput terminal 23 increases at a rate determined by the time constantCR. The voltage thus set serves as the reference wheel velocity voltage.

A comparator 40 receives the. reference voltage appearing at theterminal 23 on a negative-phase input terminal 41. A positive-phaseinput terminal 42 receives the wheel velocity voltage from the generatorthrough a voltage dividing circuit composed of resistors 44, 45 and46that divide the wheel velocity voltage and a diode 47 whose cathode andanode connect across.

the resistors 44 and 45. The comparator receives supply voltages Vcc and-'-Vcc in the same manner as the operational amplifiers and 30.

' As long as the wheel velocity voltage exceeds the forward voltage ofthe diode 47 the wheel velocity voltage at the steady state wheelvelocity is taken by the voltage dividing circuit to be a value lowerthan the actual reference wheel velocity voltage by a value which may,for example, correspond to 2 to 3 km/hr. Thus ripple componentscontained in the wheel velocity voltage in the comparator 40 do notcause errors in comparing voltages. Thus a true component of wheelvelocity voltage is compared with the reference voltage. If the wheelvelocity voltage is lower than the reference voltage or the voltageincrease rate is small the potential at the output 43 becomes Vccbecause of the voltage dividing circuit; When the opposite voltagesprevail the potential at the output terminal 43 is +Vcc.

The base of a transistor 50 receives the voltage at the output terminal43. The emitter of the transistor 50 is grounded and the collectorthereof applies its voltage to the base of a transistor 53. Thecollectorof the transistor 53 is connected to the base of a transistor51. The transistor 51 forms a free-running multivibrator with a secondtransistor 52. The base ofJa transistor 54 receives the voltageappearing at the collector of the transistor 52. The voltage +Vccenergizes the collectors of the transistors 50 through 54.

The transistors 50 and 54 serve as inverters for phase sistor 51 andholds if off while holding transistor 52 on. The conducting transistor52 turns off the transistor 54 while the multivibrator no longeroscillates.

The potential at the collector transistor 54 is now high. This highpotential is applied to the base of switching transistor 55 through thediode 60. In this case the potential at the base side of the transistor55 is divided and is lower than the voltage B applied at the collector.Nevertheless the voltage at the base is positive and causes transistor55 to conduct. As a result transistors 56, 57 and 58 are driven intononconduction.

If the potential at the output terminal 43 of the comparator 40 is +Vccthe transistor is driven into conduction and the transistor 53 is driveninto nonconduction.

The non-conduction of transistor 53 allows the multivibrator tooscillate. The potentials appearing at the diode 59 and comingintermittently through the diode 60 are applied to the base oftransistor 55. The transistor responds to the intermittent potential byturning on and off at a period determined by the multivibrator rcomposed of transistors 51 and 52. This turns the transistors 56, 57 and58 on and off.

If on the other hand, in response to a reference voltage above'thevelocity voltage as it appears at terminal 42, the potential of terminal43 is negative, transistor 50 turns off. This turns on transistor andturns off a high ignition voltage is generated by the windings 71 and 72of the ignition coil and the breaker point-73. When the transistor 58conducts the larger part of the current is by-passed by the transistor58 and the electromagnetic energy to be stored at the primary winding 71disappears. Consequently, the ignition voltage does not existat thesecondary winding during conduction 'of the transistor 58 and theignition coil is extinguished.

The operation of the circuit in FIG. 3 will be deing transistor 55. Atransistor 56 in emitter follower When the potential at the outputterminal 43 of the;

comparator 40 is Vcc the transistor 50 becomes nonconductive. This makesthe potential at its collector high so that it causes transistor 53 tobecome conduc tive. Conduction of the transistor 53 turns off thetranrepresents the wheel velocity voltage and the reference voltagep-Theabscissa represents time. Under steady state travel conditions until thetime t, the wheel velocity voltage shown by the curve A is maintained ata value lower than the reference voltage shown by the curve B. j

When the wheel is suddenly accelerated at the time t and at the time t,the acceleration exceedsthe preset acceleration, for example 0.4g",where g is the gravitational acceleration, the reference voltageincreases at the rate of 0.4g due to the increase in the wheel velocityvoltage. However, the wheel velocity voltage increases in accordancewith the acceleration applied thereto and exceeds the reference voltageat the time When the wheel velocity voltage exceeds the referencevoltage at the time t the comparator 40 constrains the transistor 58 toextinguish the ignition circuit 70 intermittently. The intermittentextinction causes the wheel velocity and its corresponding voltagegradually to decrease until it drops below the reference voltage at thetime t,,. As soon as the wheel velocity voltage drops below thereference voltage at the time t the intermittent extinguishing action isstopped. This allows the ignition circuit 70 to increase the wheelvelocity as occurred at the time However, because the precedingintermittent extinguishing action decreased the engine torque, theincrease in the rate of wheel velocity also decreases. This sets thereference voltage at a somewhat lower value.

The above described operation is repeated several times. As a result thewheel velocity gradually begins to follow the reference velocity asexpressed by the maximum reference voltage rise.

As is apparent from the above description rapid acceleration causes theanti-skid system according to this invention to control the wheelvelocity without requiring the driver to change the position of theaccclerator pedal. The anti-skid system makes the wheel velocity that israpidly being accelerated become identical to the reference velocity, asexpressed by the reference voltage, while the reference velocity followsthe critical predetermined maximum acceleration desirable as determinedby the tire and road surface condition at that time. Therefore, wheelslip due to a wheel velocity exceeding the critical acceleration ormaximum acceleration can be to a large extent almost entirely prevented.

Experiments which set the maximum or critical acceleration at 0.4g andthe timing of the multivibrator so as to produce extinguishing times of80 ms and ignition times of 30 ms during the extinction cycle of theignition circuits 70, confirm the advantageous effect of the anti-skidsystem according to this invention on slippery road surfaces such asgravel roads. The effect of the invention, however, should not belimited to the above mentioned accelerations or times.

As in FIG. 1, the system of FIG. 3 forms part of a vehicle such as anautomobile A that includes an engine, wheels, a transmission,accelerator pedal, carburator,

etc. i

For simplicity the operation of the amplifiers 20 and 30 may beconsidered another way. When the reference voltage exceeds the wheelvelocity voltage the amplifiers 20 and 30 may be considered to form aclosed negative-feedback loop. The loop includes the amplifier 30feeding through the diode 34 to the amplifier 20 which feeds back to theterminal 32. Due to the high gain of the amplifiers and the negativefeedabck, the output terminal 23 tends to drive the terminal 32 tosubstantially the same value as the wheel velocity voltage at the inputterminal 31. Since the output terminal 23 is virtually at the value ofinput terminal 32 the output reference voltage at 23 is substantiallyequal to the wheel velocity voltage.

When the wheel velocity voltage starts to exceed the reference voltage,the voltage at the output 33 of the amplifier 30 is negative and thediode cuts off the loop action. Momentarily the reference voltagecontinues to assume the last reference value which appears at the plateof charged capacitor 25 near the output 23. However, the absence of apositive voltage at input 21 allows the amplifier 20 to operate as aso-called operational integrator or Miller integrator or ramp generator.Specifically, the output 23 tends to use the negative feedback capacitor25 to force the negative bias at the input terminal 21 to assume theground potential at the input terminal 22. The capacitor can do thisonly by charging continuously at a rate RC. This raises the voltage atoutput terminal 23 at the rate RC. If the rate of rise at the wheelvelocity voltage has been less than RC the reference voltage quicklycatches up to the velocity voltage and loop operation then resumes.

By stopping and starting loop operation in this manner the referencevoltage essentially follows the velocity voltage. However, if thevelocity voltage rises at a rate greater than RC then the open loopcondition continues to exist. The reference voltage then rises only atthe rate RC starting from the value of reference voltage at which thevelocity voltage began to rise rapidly. The amplifier 40 then comparesthe voltage differences.

Operational amplifiers and operational integrators or Miller integratorsare described more fully in Pulse, Digital, and Switching Waveforms byMillman and Taub, Published 1965 by the McGraw Hill Book Company.

The comparator amplifier 40 compares the reference voltage at terminal41 with a somewhat reduced version of the wheel velocity voltage atterminal 42. When the reference voltage is greater or equal to thevelocity voltage the output of amplifier 40 is negative. This turns offtransistor 50, turns on transistors 53 and 55, and turns off transistors56, 57 and 58. This allows circuit to operate the ignition coil 71,while inhibiting oscillation in multivibrator 51, 52. When the velocityvoltage exceeds the reference voltage for a long enough time for theeffect to appear at terminal 42 the amplifier 40 turns on transistor 50,and turns off transistors 53 and 55. This releases the multivibrator andallows transistor 54 to turn the transistor 55 on and off. Transistors56, 57 and 58 turn off and on so that the operation of the inductioncoil 71 is intermittently inter rupted.

While embodiment of the invention have been described in detail it willbe obvious to those skilled in the art that the invention may beembodied otherwise without departing from its spirit and scope.

What is claimed is: i

1. An anti-skid system for a vehicle having a wheel and means foraccelerating the wheel, comprising wheel velocity generating means forgenerating a velocity signal corresponding to the velocity of the wheel,

reference means responsive to said generating means for establishing areference signal that corresponds to the velocity of the wheel andincreases at a predetermined rate when the wheel velocity signal exceedsthe predetermined rate, and comparator means responsive to saidgenerating means and said reference means for generating a comparisonsignal corresponding to the comparison of the reference signal and thevelocity signal, and control means connected to the means foraccelerating the wheel for controlling the wheel velocity in accordancewith the comparison signal, said control means including oscillatingmeans, inhibiting means responsive to said comparator means for turningsaid oscillating means on in response to a comparison signal thatindicates that the velocity signal exceeds the reference signal andturning it off at other times, and regulator means connected to themeans for accelerating the wheel for intermittently interrupting theacceleration on the basis of said oscillator means.

2. A system as in claim 1, wherein said oscillator means includes afree-running multivibrator having an output that reverses according to apredetermined time ratio.

3. A system as in claim 2, wherein said control means includes means forinterrupting operation of an ignition coil.

4. A system as in claim 2, wherein said control means includes a unitfor interrupting the fuel system of an engine.

5. A system as in claim 1, wherein said reference means includesintegrating means for establishing the reference signal and causing itto rise at the predetermined rate, said reference means furtherincluding differential circuit means responsive to the reference signaland the velocity signal for producing a differential signal and loweringthe referencesignal to the value of the velocity signal when thevelocity signal is less than the rising reference signal.

6. A system as in claim 5, wherein said control means includes means forinterrupting operation of an ignition coil.

7. A system as in claim 5, wherein said controlmeans includes a unit forinterrupting the fuel supply of an engine.

8. A system as in claim 5, wherein said integrating means includes anoperational integrator and wherein said differential circuit meansincludes a differential operational amplifier having an output connectedto the input of said operational integrator, said output including adiode.

9. A system as in claim 8, wherein said control means includes means forinterrupting operation of an ignition coil.

10. A system as in claim 8, wherein said control means includes a unitfor interrupting the fuel supply of an engine.

11. A system as in claim 2, wherein said reference means includesintegrating means for establishing the reference signal and causing itto rise at the predetermined rate, said reference means furtherincluding differential circuit means responsive to the reference signaland the velocity signal for producing a differential signal and loweringthe reference signal to the value of the velocity signal when thevelocity signal is less than the rising reference signal.

12. A system as in claim 11, wherein said integrating means includes anoperational integrator and wherein said differential circuit meansincludes a differential operational amplifier having an output connectedto the input of said operational integrator, said output including adiode.

13. A system as in claim 12, wherein said control means includes meansfor interrupting operation of an ignition coil.

14. A system as in claim 12, wherein said control means includes a unitfor interrupting the fuel supply of an engine.

15. A system as in claim 11, wherein said control means includes meansfor interrupting operation of an ignition coil.

16. A system as in claim 11, wherein said control means includes a unitfor interrupting the fuel supply of an engine.

17. A system as in claim 1, wherein said control means includes meansfor interrupting operation of an ignition coil.

18. A system as in claim I, wherein said control means includes a unitfor interrupting the fuel supply of an engine. I

19. An anti-skid system for a vehicle having a wheel and means foraccelerating the wheel, comprising reference means for generating areference velocity signal rising at a predetermined rate, comparisonmeans responsive to said reference means and the wheel for comparing thevelocity of the wheel with the reference velocity and for lowering thereference signal to the wheel velocity when the wheel velocity is lowerthan the reference velocity, and means responsive to said comparisonmeans for inhibiting the operation of the means to accelerate the wheel,said control means including oscillating means, inhibiting meansresponsive to said comparator means for turning said oscillating meanson in response to a comparison signal that indicates that the velocitysignal exceeds the reference signal and turning it off at other times,and regulator means connected to the means for accelerating the wheelfor intermittently interrupting the acceleration on the basis of saidoscillator means.

20. A system as in claim 19, wherein said oscillator means includes afree-running multivibrator having an output that reverses according to apredetermined time ratio.

21. A system as in claim 19, wherein said reference means includesintegrating means for establishing the reference signal and causing itto :rise at the predetermined rate, said reference means furtherincluding differential circuit means responsive to the reference signaland the velocity signal for producing a differential signal and loweringthe reference signal to the value of the velocity signal when thevelocity signal is less thanthe rising reference signal.

22. A system as in claim 19, wherein said integrating means includes anoperational integrator and wherein said differential circuit meansincludes a differential operational amplifier having an output connectedto the input of said operational integrator, said output including adiode.

23. A system as in claim 20, wherein said reference means includesintegrating means for establishing the reference signal and causing itto rise at the predetermined rate, said reference means furtherincluding differential circuit means responsive to the reference signaland the velocity signal for producing a differential signal and loweringthe reference signal to the value of the velocity signal when thevelocity signal is less than the rising reference signal.

24. A system as in claim 20 wherein said integrating means includes anoperational integrator and wherein said differential circuit meansincludes a differential operational amplifier having an output connectedto the input of said operational integrator, said output including adiode, said reference means includes integrating means for establishingthe reference signal and causing it to rise at the predetermined rate,said reference means further including difierential circuit meansresponsive to the reference signal at the velocity signal for producinga differential, signal and lowering the reference signal to the value ofthe velocity signal when the velocity signal is less than the risingreference sig nal.

25. A system as in claim 20, wherein said integrating means includes anoperational integrator and wherein said differential circuit meansincludes a differential operational amplifier having an output connectedto the input of said operational integrator, said output including adiode.

26. A system as in claim 19, wherein said control means includes meansfor in terrupting operation of an ignition coil.

27. A system as in claim 19, wherein said control means includes a unitfor interrupting the fuel supply of an engine.

28. A vehicle comprising an engine, wheels, accelerating means foraccelerating the velocity of the wheel, reference means for establishinga velocity reference signal that rises at a predetermined value,comparison means for comparing the velocity of one of said wheels withthe reference velocity and for lowering the reference velocity to thevalue of the wheel velocity, and control means responsive to saidcomparison means for regulating said accelerating means so as to slowthe wheel velocity when the wheel velocity is rising faster than thereference velocity, said control means including oscillating means,inhibiting means responsive to said comparator means for turning saidoscillating means on in response to a comparison signal that indicatesthat the velocity signal exceeds the reference signal and turning it offat other times, and regulator means connected to the means foraccelerating the wheel for intermittently interrupting the accelerationon the basis of said oscillator means.

29. A system as in claim 28, wherein said oscillator means includes afree-running multivibrator having an output that reverses according to apredetermined time ratio.

30. A system as in claim 29, wherein said reference means includesintegrating means for establishing the reference signal and causing itto rise at the predetermined rate, said reference means furtherincluding differential circuit means responsive to the reference signaland the velocity signal for producing a differential signal and loweringthe reference signal to the value of the velocity signal when thevelocity signal is less than the rising reference signal.

31. A system as in claim 29 wherein said integrating means includes anoperational integrator and wherein said differential circuit meansincludes a differential operational amplifier having an output connectedto the input of said operational integrator, said output including adiode, said reference means includes integrating means for establishingthe reference signal and causing it to rise at the predetermined rate,said reference means further including differential circuit meansresponsive to the reference signal and the velocity signal for producinga differential signal and lowering the reference signal to the value ofthe velocity signal when the velocity signal is less than the risingreference signal.

32. A system as in claim 29, wherein said integrating means includes anoperational integrator and wherein said differential circuit meansincludes a differential operational amplifier having an output connectedto the input of said operational integrator, said output insignal andlowering the reference signal to the value of the velocity signal whenthe velocity signal is less than the rising reference signal.

34. A system as in claim 28, wherein said integrating means includes anoperational integrator and wherein said differential circuit meansincludes a differential operational amplifier having an output connectedto the input of said operational integrator, said output including adiode.

35. A vehicle comprising an engine, at least one wheel responsive to theengine, accelerator means for causing said engine to accelerate thevelocity of the wheel, wheel velocity generating means responsive to therotation of the wheel for generating a velocity signal corresponding tothe velocity of the wheel, reference means responsive to said generatingmeans for establishing a reference signal that corresponds to thevelocity of the wheel and increases at a predetermined rate when thewheel velocity signal exceeds the predetermined rate, and comparatormeans responsive to said generating means and said reference means forgenerating a comparison signal when the velocity signal rises at a ratefaster than the reference signal, and control means connected to theaccelerating means for slowing the wheel velocity so that it increasesat a rate up to the increase of the reference signal, said control meansincluding oscillating means, inhibiting means responsive to saidcomparator means for turning said oscillating means on in response to acomparison signal that indicates that the velocity signal exceeds thereference signal and turning it off at other times, and regulator meansconnected to the means for accelerating the wheel for intermittentlyinterrupting the acceleration on the basis of said oscillator means.

36. A system as in claim 35, wherein said oscillator means includes afree-running multivibrator having an output that reverses according to apredetermined time ratio.

37. A system as in claim 35, wherein said reference means includesintegrating means for establishing the reference signal and causing itto rise at the predetermined rate, said reference means furtherincluding differential circuit means responsive to the reference signaland the velocity signal for producing a difierential signal and loweringthe reference signal to the value of the velocity signal when thevelocity signal is less than the rising reference signal.

38. A system as in claim 35, wherein said integrating means includes anoperational integrator and wherein said differential circuit meansincludes a differential operational amplifier having an output connectedto the input of said operational integrator, said output in cluding adiode.

39. A system as in claim 35, wherein said reference means includesintegrating means for establishing the reference signal and causing itto rise at the predetermined rate, said reference means furtherincluding differential circuit means responsive to the reference signaland the velocity signal for producing a differential signal and loweringthe reference signal to the value of the velocity signal when thevelocity signal is less than the rising reference signal.

40. A system as in claim 35, wherein said integrating means includes anoperational integrator and wherein said differential circuit meansincludes a difi'erential operational amplifier having an outputconnected to the input of said operational integrator, said outputinnal.

41. A system as in claim 35, wherein said control means includes meansfor interrupting operation of an ignition coil.

42. A system as in claim 35 wherein said control means includes a unitfor interrupting the fuel supply of an engine.

1. An anti-skid system for a vehicle having a wheel and means foraccelerating the wheel, comprising wheel velocity generating means forgenerating a velocity signal corresponding to the velocity of the wheel,reference means responsive to said generating means for establishing areference signal that corresponds to the velocity of the wheel andincreases at a predetermined rate when the wheel velocity signal exceedsthe predetermined rate, and comparator means responsive to saidgenerating means and said reference means for generating a comparisonsignal corresponding to the comparison of the reference signal and thevelocity signal, and control means connected to the means foraccelerating the wheel for controlling the wheel velocity in accordancewith the comparison signal, said control means including oscillatingmeans, inhibiting means responsive to said comparator means for turningsaid oscillating means on in response to a comparison signal thatindicates that the velocity signal exceeds the reference signal andturning it off at other times, and regulator means connected to themeans for accelerating the wheel for intermittently interrupting theacceleration on the basis of said oscillator means.
 2. A system as inclaim 1, wherein said oscillator means includes a free-runningmultivibrator having an output that reverses according to apredetermined time ratio.
 3. A system as in claim 2, wherein saidcontrol means includes means for interrupting operation of an ignitioncoil.
 4. A system as in claim 2, wherein said control means includes aunit for interrupting the fuel system of an engine.
 5. A system as inclaim 1, wherein said reference means includes integrating means forestablishing the reference signal and causing it to rise at thepredetermined rate, said reference means further including differentialcircuit means responsive to the reference signal and the velocity signalfor producing a differential signal and lowering the reference signal tothe value of the velocity signal when the velocity signal is less thanthe rising reference signal.
 6. A system as in claim 5, wherein saidcontrol means includes means for interrupting operation of an ignitioncoil.
 7. A system as in claim 5, wherein said control means includes aunit for interrupting the fuel supply of an engine.
 8. A system as inclaim 5, wherein said integrating means includes an operationalintegrator and wherein said differential circuit means includes adifferential operational amplifier having an output connected to theinput of said operational integrator, said output including a diode. 9.A system as in claim 8, wherein said control means includes means forinterrupting operation of an ignition coil.
 10. A system as in claim 8,wherein said control means includes a unit for interrupting the fuelsupply of an engine.
 11. A system as in claim 2, wherein said referencemeans includes integrating means for establishing the reference signaland causing it to rise at the predetermined rate, said reference meansfurther including differential circuit means responsive to the referencesignal and the velocity signal for producing a differential signal andlowering the reference signal to the value of the velocity signal whenthe velocity signal is less than the rising reference signal.
 12. Asystem as in claim 11, wherein said integrating means includes anoperational integrator and wherein said differential circuit meansincludes a differential operational amplifier having an output connectedto the input of said operational integrator, said output including adiode.
 13. A system as in claim 12, wherein said control means includesmeans for interrupting operation of an ignition coil.
 14. A system as inclaim 12, wherein said control means includes a unit for interruptingthe fuel supply of an engine.
 15. A system as in claim 11, wherein saidcontrol means includes means for interrupting operation of an ignitioncoil.
 16. A system as in claim 11, wherein said control means includes aunit for interrupting the fuel supply of an engine.
 17. A system as inclaim 1, wherein said control means includes means for interruptingoperation of an ignition coil.
 18. A system as in claim 1, wherein saidcontrol means includes a unit for interrupting the fuel supply of anengine.
 19. An anti-skid system for a vehicle having a wheel and meansfor accelerating the wheel, comprising reference means for generating areference velocity signal rising at a predetermined rate, comparisonmeans responsive to said reference means and the wheel for comparing thevelocity of the wheel with the reference velocity and for lowering thereference signal to the wheel velocity when the wheel velocity is lowerthan the reference velocity, and means responsive to said comparisonmeans for inhibiting the operation of the means to accelerate the wheel,said control means including oscillating means, inhibiting meansresponsive to said comparator means for turning said oscillating meanson in response to a comparison signal that indicates that the velocitysignal exceeds the reference signal and turning it off at other times,and regulator means connected to the means for accelerating the wheelfor intermittently interrupting the acceleration on the basis of saidoscillator means.
 20. A system as in claim 19, wherein said oscillatormeans includes a free-running multivibrator having an output thatreverses according to a predetermined time ratio.
 21. A system as inclaim 19, wherein said reference means includes integrating means forestablishing the reference signal and causing it to rise at thepredetermined rate, said reference means further including differentialcircuit means responsive to the reference signal and the velocity signalfor producing a differential signal and lowering the reference signal tothe value of the velocity signal when the velocity signal is less thanthe rising reference signal.
 22. A system as in claim 19, wherein saidintegrating means includes an operational integrator and wherein saiddifferential circuit means includes a differential operational amplifierhaving an output connected to the input of said operational integrator,said output including a diode.
 23. A system as in claim 20, wherein saidreference means includes integrating means for establishing thereference signal and causing it to rise at the predetermined rate, saidreference means further including differential circuit means responsiveto the reference signal and the velocity signal for producing adifferential signal and lowering the reference signal to the value ofthe velocity signal when the velocity signal is less than the risingreference signal.
 24. A system as in claim 20 wherein said integratingmeans includes an operational integrator and wherein said differentialcircuit means includes a differential operational amplifier having anoutput connected to the input of said operational integrator, saidoutput including a diode, said reference means includes integratingmeans for establishing the reference signal and causing it to rise atthe predetermined rate, said reference means further includingdifferential circuit means responsive to the reference signal at thevelocity signal for producing a differential signal and lowering thereference signal to the value of the velocity signal when the velocitysignal is less than the rising reference signal.
 25. A system as inclaim 20, wherein said integrating means includes an operationalintegrator and wherein said differential circuit means includes adifferential operational amplifier having an output connected to theinput of said operational integrator, said output including a diode. 26.A system as in claim 19, wherein said control means includes means forin terrupting operation of an ignition coil.
 27. A system as in claim19, wherein said control means includes a unit for interrupting the fuelsupply of an engine.
 28. A vehicle comprising an engine, wheels,accelerating means for accelerating the velocity of the wheel, referencemeans for establishing a velocity reference signal that rises at apredetermined value, comparison means for comparing the velocity of oneof said wheels with the reference velocity and for lowering thereference velocity to the value of the wheel velocity, and control meansresponsive to said comparison means for regulating said acceleratingmeans so as to slow the wheel velocity when the wheel velocity is risingfaster than the reference velocity, said control means includingoscillating means, inhibiting means responsive to said comparator meansfor turning said oscillating means on in response to a comparison signalthat indicates that the velocity signal exceeds the reference signal andturning it off at other times, and regulator means connected to themeans for accelerating the wheel for intermittently interrupting theacceleration on the basis of said oscillator means.
 29. A system as inclaim 28, wherein said oscillator means includes a free-runningmultivibrator having an output that reverses according to apredetermined time ratio.
 30. A system as in claim 29, wherein saidreference means includes integrating means for establishing thereference signal and causing it to rise at the predetermined rate, saidreference means further including differential circuit means responsiveto the reference signal and the velocity signal for producing adifferential signal and lowering the reference signal to the value ofthe velocity signal when the velocity signal is less than the risingreference signal.
 31. A system as in claim 29 wherein said integratingmeans includes an operational integrator and wherein said differentialcircuit means includes a differential operational amplifier having anoutput connected to the input of said operational integrator, saidoutput including a diode, said reference means includes integratingmeans for establishing the reference signal and causing it to rise atthe predetermined rate, said reference means further includingdifferential circuit means responsive to the reference signal and thevelocity signal for producing a differential signal and lowering thereference signal to the value of the velocity signal when the velocitysignal is less than the rising reference signal.
 32. A system as inclaim 29, wherein said integrating means includes an operationalintegrator and wherein said differential circuit means includes adifferential operational amplifier having an output connected to theinput of said operational integrator, said output including a diode. 33.A system as in claim 28, wherein said reference means includesintegrating means for establishing the reference signal and causing itto rise at the predetermined rate, said reference means furtherincluding differential circuit means responsive to the reference signaland the velocity signal for producing a differential signal and loweringthe reference signal to the value of the velocity signal when thevelocity signal is less than the rising reference signal.
 34. A systemas in claim 28, wherein said integrating means includes an operationalintegrator and wherein said differential circuit means includes adifferential operational amplifier having an output connected to theinput of said operational integrator, said output including a diode. 35.A vehicle comprising an engine, at least one wheel responsive to theengine, accelerator means for causing said engine to accelerate thevelocity of the wheel, wheel velocity generating means responsive to therotation of the wheel for generating a velocity signal corresponding tothe velocity of the wheel, reference means responsive to said generatingmeans for establishiNg a reference signal that corresponds to thevelocity of the wheel and increases at a predetermined rate when thewheel velocity signal exceeds the predetermined rate, and comparatormeans responsive to said generating means and said reference means forgenerating a comparison signal when the velocity signal rises at a ratefaster than the reference signal, and control means connected to theaccelerating means for slowing the wheel velocity so that it increasesat a rate up to the increase of the reference signal, said control meansincluding oscillating means, inhibiting means responsive to saidcomparator means for turning said oscillating means on in response to acomparison signal that indicates that the velocity signal exceeds thereference signal and turning it off at other times, and regulator meansconnected to the means for accelerating the wheel for intermittentlyinterrupting the acceleration on the basis of said oscillator means. 36.A system as in claim 35, wherein said oscillator means includes afree-running multivibrator having an output that reverses according to apredetermined time ratio.
 37. A system as in claim 35, wherein saidreference means includes integrating means for establishing thereference signal and causing it to rise at the predetermined rate, saidreference means further including differential circuit means responsiveto the reference signal and the velocity signal for producing adifferential signal and lowering the reference signal to the value ofthe velocity signal when the velocity signal is less than the risingreference signal.
 38. A system as in claim 35, wherein said integratingmeans includes an operational integrator and wherein said differentialcircuit means includes a differential operational amplifier having anoutput connected to the input of said operational integrator, saidoutput including a diode.
 39. A system as in claim 35, wherein saidreference means includes integrating means for establishing thereference signal and causing it to rise at the predetermined rate, saidreference means further including differential circuit means responsiveto the reference signal and the velocity signal for producing adifferential signal and lowering the reference signal to the value ofthe velocity signal when the velocity signal is less than the risingreference signal.
 40. A system as in claim 35, wherein said integratingmeans includes an operational integrator and wherein said differentialcircuit means includes a differential operational amplifier having anoutput connected to the input of said operational integrator, saidoutput including a diode, said reference means includes integratingmeans for establishing the reference signal and causing it to rise atthe predetermined rate, said reference means further includingdifferential circuit means responsive to the reference signal and thevelocity signal for producing a differential signal and lowering thereference signal to the value of the velocity signal when the velocitysignal is less than the rising reference signal.
 41. A system as inclaim 35, wherein said control means includes means for interruptingoperation of an ignition coil.
 42. A system as in claim 35 wherein saidcontrol means includes a unit for interrupting the fuel supply of anengine.